(a) Field of the Invention
The present invention relates to an apparatus for measuring flatness of hot rolled strips in a rolling mill and, more particularly, to a contact-typed strip flatness measuring device which protects load sensors from heat or impact while controlling surface points of split rolls to move up and down.
(b) Description of the Related Art
Generally, metal strips produced through hot-rolling slabs should be kept to be even in flatness along the width thereof.
An automatic shape controller based on a shapemeter has been frequently employed for use in controlling the strip flatness during the hot rolling process. FIG. 1 illustrates a rolling mill with such an automatic shape controller. In the automatic shape controller, a shapemeter 1 measures the shape change in the target hot rolled strip S through generating laser, and detects the strip flatness based on the measured shape change. The detected value of the strip flatness is input into a calculator 4 that calculates a control value. Then, depending upon the control value, a bender controlling unit 5 controls pressure of a bender 2 installed at the last stand, thereby controlling the strip flatness.
However, in the above strip flatness control technique, the strip flatness is basically controlled by taking the shape change of the hot rolled strip S as a criterion, and such a shape change largely differs from the practical value of strip flatness. Therefore, in such a technique, the strip flatness cannot be measured in a correct manner. Furthermore, when the frontal end portion of the hot rolled strip S transported over a roller table 3 is coiled around a coiler 6, the hot rolled strip S is flattened under strain due to the difference in relative speeds between the last stand B and the coiler 6. Accordingly, the shapemeter 1 cannot measure the strip flatness after the hot rolled strip S is coiled around the coiler 6.
In order to solve such problems, a contact-type strip flatness measuring device has been suggested. In the device, the strip flatness is measured through detecting reduction in the hot rolled strip while directly contacting it.
Split looper rolles are arranged along the width of the hot rolled strip S, and a load sensor is attached to each split roll to detect load distribution of the hot rolled strip S. The detected load distribution is converted to a value of strip flatness, and makes feedback to a flatness control system, thereby controlling flatness across the hot rolled strip S.
When the load distribution signal issued from the strip flatness measuring device makes feedback to the flatness control system on line, uniform flatness can be obtained over the entire length of the hot rolled strip S.
However, such a contact-type load distribution measuring device should perform its intrinsic functions in poor working conditions such as high temperature, high humidity, and high vibration. Furthermore, it should ensure sufficient device stability and reliability, and detect the load distribution in a stable manner.
FIG. 2 illustrates a contact-type strip flatness measuring device installed at the Hoesch steel mill of German (Herman J. Kopineck, xe2x80x9cRolling of hot strips with controlled Tension and Flatness,xe2x80x9d Hot strip profile and flatness seminar, Nov. 2-3, 1988, Pittsburg Pa.). As shown in FIG. 2, a load sensor 12 is provided at an end portion of a support 11 bearing a split roll 10 to detect the load applied to the split roll 10, thereby measuring the strip flatness.
However, in such a device, since the difference in the maximum loads at tension and compression (hereinafter referred to as the xe2x80x9cpeak loadxe2x80x9d) is so great that the load sensor 12 is liable to be broken at repeated sensing operations, resulting in lowered precision and reduced device life span.
FIG. 3 illustrates another contact-type measuring device disclosed by George. F. Kelk in xe2x80x9cNew developments improve hot strip: Shapemeter-Looper and Shape Actimeterxe2x80x9d, Iron and Steel Eng., August, 1986, pp. 48-56. As shown in FIG. 3, a compression-type load sensor 22 is provided at the bottom side of a shaft support 21 bearing a split roll 20. In this structure, the tensile load applied to the split roll 20 does not influence the load sensor 22 so that the peak load can be reduced. However, since the strip flatness measuring device should play its intrinsic functions as a looper before it detects the load applied to the hot rolled strip S along the width thereof, the looper excessively moves up and down when uneveness in mass between the neighboring stands is present due to the great difference in relative speeds between the stands. In this case, the looper collides with an upper or lower damper so that strong impact is applied to the strip flatness measuring device, resulting in reduced life span of the load sensor 22.
In this connection, a stopper 23 is provided at the strip flatness measuring device to prevent the load sensor 22 from being applied with an over-load.
However, when the maximum load is applied to the load sensor 22, the compressed displacement is too small to make sufficient distance for preventing the load sensor 22 from being applied with the over-load. Thus, the mechanical means of protecting the load sensor 22 based on the stopper 23 has a limit in application in that whenever the device suffers slight deformation, the stopper 23 should be controlled each time.
Furthermore, the strip flatness measuring devices shown in FIGS. 2 and 3 are interposed between the rolling stands, and the temperature of the hot rolled strips S amounts to 800 to 1200xc2x0 C. In these conditions, the load sensor extremely sensitive to heat should be protected from the heat in a stable manner. If not, errors in meaurement are inevitably followed by.
For that reason, a cooling nozzle 24 is provided at the strip flatness measuring device to spray cooling water to the load sensor 22. However, in case the spraying of the cooling water becomes poor due to breakage or alien materials, there is a problem in that the preparation for such a case is absent.
Furthermore, the hot rolled strips are differentiated in the load distribution depending upon their shapes. Therefore, when the strip flatness measuring device is used for a long time, the plural numbers of split rolls 10 and 20 are rubbed in a different manner so that they become differentiated in horizontal height, and errors in detection with respect to the load applied thereto are made.
In order to solve such a problem, the strip measuring device shown in FIG. 2 is provided with a height control bolt 13 for controlling the tangent-movement thereof around a rotation shaft 14, and the strip measuring device shown in FIG. 3 with a wedge-shaped control member 25 for controlling the tangent-movement.
However, in such a case, as shown in FIG. 4A, deviation in rubbing dR between the split rolls 10 and 20 is made. Even though such a deviation in rubbing is controlled, as shown in FIG. 4B, deviance in controlling dRxe2x80x2 is present so that the load sensors 12 and 22 for detecting the load applied to the hot rolled strip S incorrectly detect such a load while making serious errors in the flatness detection signal. That is, in the one-directional control technique, the horizontal height of the measuring device cannot be controlled in a correct manner.
Meanwhile, in case the rubbed split rolls should be repaired or replaced by a new one, long repair or replacement time is required, lowering productivity.
It is an object of the present invention to provide a strip flatness measuring device which can protect a load sensor from the external factors, and control the relative heights between split rolls while securing precesion in measurement.
This and other objects may be achieved by a strip flatness measuring device including a looper with a plurality of split rolls. The split rolls are assembled in a bracket such that each split roll can be separated from the bracket. A normal-movement control unit for moving the split rolls in the normal direction, a tangent-movement control unit for moving the split rolls in the tanget direction are provided at a side of the bracket. A support is movably connected to the tanget-movement control unit, and an impact absorption unit is installed at the support. A sensor cap is installed at a side of the support while pressurizing a load sensor. A pre-pressure application unit is provided between the support and a base of the looper to previously compresses the sensor cap against the load sensor, thereby preventing the load sensor from being released from the sensor cap.
In the above structure, even though deviation in rubbing occurs at the split rolls, the normal-movement control unit and the tangent-movement control units can precisely control the relative heights between the split rolls.
Furthermore, the load sensor is protected from the external impacts by way of the impact absorption unit and the pre-pressure application unit so that it can detect load distribution in a stable manner. The load sensor is also protected from the heat through mounting a heat-shielding ring around the load sensor.